ARM: 8222/1: mvebu: enable strex backoff delay

Under extremely rare conditions, in an MPCore node consisting of at
least 3 CPUs, two CPUs trying to perform a STREX to data on the same
shared cache line can enter a livelock situation.

This patch enables the HW mechanism that overcomes the bug. This fixes
the incorrect setup of the STREX backoff delay bit due to a wrong
description in the specification.

Note that enabling the STREX backoff delay mechanism is done by
leaving the bit *cleared*, while the bit was currently being set by
the proc-v7.S code.

[Thomas: adapt to latest mainline, slightly reword the commit log, add
stable markers.]

Fixes: de490193 ("arm: mm: Add support for PJ4B cpu and init routines")

Cc: <stable@vger.kernel.org> # v3.8+
Signed-off-by: Nadav Haklai <nadavh@marvell.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/proc-v7.S

@@ -270,7 +270,6 @@ __v7_pj4b_setup:
 /* Auxiliary Debug Modes Control 1 Register */
 #define PJ4B_STATIC_BP (1 << 2) /* Enable Static BP */
 #define PJ4B_INTER_PARITY (1 << 8) /* Disable Internal Parity Handling */
-#define PJ4B_BCK_OFF_STREX (1 << 5) /* Enable the back off of STREX instr */
 #define PJ4B_CLEAN_LINE (1 << 16) /* Disable data transfer for clean line */
 
 /* Auxiliary Debug Modes Control 2 Register */
@@ -293,7 +292,6 @@ __v7_pj4b_setup:
 	/* Auxiliary Debug Modes Control 1 Register */
 	mrc	p15, 1,	r0, c15, c1, 1
 	orr     r0, r0, #PJ4B_CLEAN_LINE
-	orr     r0, r0, #PJ4B_BCK_OFF_STREX
 	orr     r0, r0, #PJ4B_INTER_PARITY
 	bic	r0, r0, #PJ4B_STATIC_BP
 	mcr	p15, 1,	r0, c15, c1, 1